In die transfer systems of the subject character, a finger bar extends along one or both lateral sides of the die stations of a stamping press, and fingers extend inwardly from the finger bar or bars for engaging workpieces at the successive die stations. The finger bar or bars are driven longitudinally and laterally in synchronism with operation of the press for transferring workpieces through successive die stations and then out of the die. U.S. Pat. Nos. 4,032,018 and 5,307,666 each disclose die transfer systems of this general character, in which the finger bars are mechanically coupled by cam-and-follower arrangements to the ram of the stamping press for controlling operation of the finger bars.
U.S. application Ser. No. 08/280,089, assigned to the assignee hereof, discloses a die transfer system in which the drive mechanism for moving the fingers laterally into and out of engagement with the workpieces comprises at least two finger bar drive modules coupled to the finger bar and spaced from each other lengthwise of the finger bar. A drive shaft extends between and interconnects the two drive modules. Each of the drive modules includes a crank arm coupled to the drive shaft for rotating the crank arm about an axis parallel to the finger bar. A cam plate is coupled to the finger bar and mounted for movement lateral to the crank arm axis and the finger bar. The cam plate has orthogonal interconnected slots each extending in a direction lateral to the crank arm axis. A cam follower is mounted on the crank arm and disposed in the slots, such that rotation of the drive shaft rotates the crank arm and propels the cam follower along the cam plate slots in sequence so as to move the cam plate and the finger bar sequentially horizontally and vertically with respect to the die stations. The drive shaft is rotated in synchronism with operation of the stamping press, preferably by an electric servo motor and motor controller coupled to a sensor for monitoring position of the stamping press.
Although the die transfer systems disclosed in the noted patents and pending application have enjoyed commercial acceptance and success, further improvements remain desireable. For example, in the transfer system disclosed in the noted co-pending application, the point of maximum velocity and maximum torque on the crank arm, drive shaft and motor are at the point of transition between horizontal and vertical motions at the finger bar. Such an arrangement produces undesirably high loads on the drive motor, shaft and associated components, such as the shaft bearings and transfer gears. Motion at the finger bar is essentially continuous as the crank arm rotates and the cam follower moves through the cam plate slots. Also, in the system disclosed in the pending application, there is a cam lock arrangement provided for preventing reverse horizontal movement of the finger bar and cam plate during vertical motion, which requires addition components and assembly time, thus undesirably increasing the cost of manufacture. It is a general object of the present invention to provide a modular die transfer system of the subject character that addresses one or more of these undesirable features of the prior art.